Application of Continuous-Wave Cavity Ring-Down Spectroscopy to Laminar Flames

In this paper, we describe the application of diode-laser continuous-wave cavity ring-down spectroscopy (cw-CRDS) to in-situ flame diagnostics. Spectra of the P17e acetylene feature at 1535.4 nm were recorded in a premixed laminar ethylene/air flame. The overall absorption of the feature was measured to be
$\approx\!\!1.5\times 10^{-4}\ \text{cm}^{-1}$
, which is a short distance above the reaction zone for a flame fuel equivalence ratio of 1.66, and the minimum detection limit
$(3\sigma)$
of the system was calculated to be
$1.2\times 10^{-5}\ \text{cm}^{-1}$
. This demonstrates the potential of the technique for the measurement of weakly absorbing species in flames. Finally, we discuss the advantages and limitations of the cw-CRDS technique for flame measurements.